The present invention relates generally to carburetors for internal combustion engines, and more specifically to carburetor primer mechanisms especially for use in diaphragm-type carburetors.
In small internal combustion engines, and in particular those engines which are started by hand cranking, it is frequently desirable to prime the engine by introducing a fuel-rich mixture into the engine intake system to aid in starting the engine. Such priming arrangements are particularly desirable for use in internal combustion engines of the type which are commonly used in lawnmowers, snow throwers, chain saws and the like, that are likely to be started either infrequently, or in cold weather.
Known priming arrangements are frequently in the form of an operator actuable bulb which, when depressed, displaces a volume of air into the air space above a carburetor float bowl fuel well. This air exerts a pressure on the fuel which forces the fuel upwardly through a conduit into a venturi where it is mixed with air and then drawn into the intake manifold of the engine.
For diaphragm carburetors in which the priming system is the only means for cold start enrichment of the engine, large volume displacement is desirable for purging a fuel system that has been run dry of fuel or never had fuel in it. An example of a typical diaphragm carburetor is disclosed in U.S. Pat. No. 4,684,484, issued to Guntly, assigned to the assignee of the present invention and incorporated herein by reference. In order to provide the volume displacement necessary for purging a completely dry fuel system, large volume priming bulbs can be utilized. However, once the fuel system or carburetor has been initially purged, continued use of the large volume primer may result in overenrichment and engine flooding. Therefore, it is desired to provide a priming system that renders the proper amount of priming fuel to the carburetor under various starting conditions.